** Shares of cancer drugmaker Verastem VSTM.O rise 45.7% to $5.35 premarket

** On Monday, VSTM said the U.S. FDA granted Priority Review to its application for its experimental cancer therapy, avutometinib in combination with defactinib

** Drugmaker sought approval for the combo therapy for patients with recurrent low-grade serous ovarian cancer who have a KRAS gene mutation and have received at least one prior systemic therapy

** Priority Review designation means FDA's goal is to take action on an application within 6 months, compared to 10 months under standard review

** Analysts at BTIG say total addressable market for the condition is over $1.7 bln, based on around 2,800 patients in the first 3 to 5 years

** Brokerage also has increased the probability of success for the treatment from 65% to 80%, raising PT from $13 to $20, representing a 5x upside to the stock's Monday close

** Brokerage B. Riley Securities notes VSTM is "fundamentally undervalued"

** The FDA will give its decision on June 30, 2025 - VSTM

** FDA is not currently planning to hold an advisory committee meeting to discuss the application - VSTM

** Co said it is preparing for commercial launch in mid-2025

** As of last close, stock has fallen ~55% YTD

(Reporting by Kamal Choudhury in Bengaluru)

((Kamal.Choudhury@thomsonreuters.com;))